The invention relates to a directing apparatus for guiding, deflecting and/or diverting a web of material which is guided over a number of rollers, said apparatus being connected to a medium supply device. More particularly, the invention relates to such an apparatus in which the directing apparatus extends over the entire width of the rollers and has bores, through which a stream of medium flows against the web of material in a direction which is predetermined in each case.
German Offenlegungsschrift 3,904,314 discloses such an air directing apparatus for guiding an endless web of material, for example a web of paper, which runs in a meandering manner over a plurality of cylinders or alternately over cylinders and directing rollers. This air directing apparatus is connected to a blown air supply and extends transversely over the entire width of the cylinder and directing rollers, air being blown against the web of material via blow openings extending in the predetermined direction. The blowing direction of the air is reversible, with the reversal taking place by two successive pressure chambers which are separate from each other and of which one acts in normal operation as a suction chamber and the downstream one acts as a blowing chamber. These chambers are switchable in such a way that the pressure chamber on the feed side is made to act as a blowing chamber and the downstream pressure chamber is made to act as a suction chamber. The air directing apparatus can also be divided transversely to the running direction of the web of material into a number of separate air chambers. In this case, a chamber at the edge is provided for transferring a transfer strip during starting or after a tearing-off of material. Each air chamber can be set individually with respect to the blowing direction, according to the predetermined blowing direction or the direction inverted or perpendicular thereto. Similarly, the quantities of air can be set according to the blowing direction.
By the known air directing apparatus, on the one hand, the endless web of material is guided reliably on its path to and between the cylinders and/or the directing rollers. On the other hand, the known apparatus maximizes the conditioning of the web of material, for example its drying.
In the normal operation of a paper machine, the web of paper runs from cylinder to cylinder. The air directing apparatus counteracts the forces acting on the web due to adhesion, friction, vacuum, dynamic pressure, the weight of the web, and centrifugal forces. In this case it must be taken into consideration that with such air directing apparatuses, it also intended to achieve an optimum drying effect. An optimum drying effect is achieved if air is blown out against the running direction of the web of paper, since this has the effect of producing turbulence on the surface of the web of paper, which accelerates the drying. However, during starting of a paper machine or after a tearing-off of the web of paper during threading of the so-called transfer strip, such a blowing direction against the running direction of the web of paper is unfavorable, since the relatively narrow transfer strip is blown away by the blow jet on account of its relatively small weight. In the case of the known air directing apparatus, an individual adaptation of the direction and conditions of the blown air to the respective operating state and the respective type of material is possible by virtue of the fact that the blowing direction can be inverted and, what is more, the web of paper can be subjected to the blowing of air in different sections, considered in the running direction.
German Offenlegungsschrift 4,003,956 discloses a vacuum nozzle system for the contactless supporting and treating of webs of material, for example for drying, heating and cooling. This vacuum system comprises a nozzle casing which has a surface which lies against the web and on which there are two nozzle gaps. The nozzle system is asymmetrical in relation to the perpendicular center plane of the vacuum supporting surface. The nozzle casing has a substantially planar supporting surface, at the one edge of which an arcuate Coanda air directing surface is attached, at which the first nozzle of the nozzle system is located. The blowing direction of this nozzle initially runs substantially perpendicularly against the plane of the web of material to be supported. The Coanda air directing surface is arranged in such a way that it diverts the air flow emerging from the first nozzle in the direction of the plane of the supporting surface and the web of material running over the latter. In the edge region opposite the first nozzle there is a directing baffle which smoothly continues the planar supporting surface. A second blowing nozzle is arranged in the region of or at the outer edge of the directing surface. The direction of the second nozzle runs parallel to the directing surface of the supporting surface.
An apparatus for monitoring the edge of the web of a guided web of material is described in German Offenlegungsschrift 3,903,783. This concerns an apparatus for conveying a flat article, in particular an endless web of material. The apparatus comprises conveying means for moving the article in a predetermined direction and a monitoring device for monitoring the position of the article. The monitoring device includes a blowing nozzle which is directed at the edge region of the surface of the article and blows out a jet of gas. On the side of the article opposite the blowing nozzle there is provided a pressure measuring device for generating a measuring signal corresponding to the proportion of the gas jet flowing past the edge. The pressure measuring device is connected to an evaluating and controlling arrangement for processing the measuring signals into position signals, which reproduce the position of the edge of the article. Such an apparatus permits an exact processing and working of articles since a web of material such as paper or some other flat article can be conveyed along a predetermined path while preventing lateral positional deviations. This is performed by the continuous monitoring of the position of an edge of the above material or of the flat article and by corrective measures being initiated if deviations from a predetermined position of the edge occur. By this side-edge control, consequently, a lateral shifting of the article is prevented.
Side-edge controls are also known in which the unwinding reel for the web of material is displaced axially or the angle of a directing roller perpendicular to a web plane is altered. Both versions require greater mechanical complexity and are limited in their dynamic characteristics.